Food and feeding ecology of postlarval and juvenile Pleuragramma antarcticum (Pisces; Notothenioidei) in the seasonal pack ice zone off the Antarctic peninsula

Abstract

Stomach contents of 275 postlarval and 269 one year old juvenile Pleuragramma antarcticum caught in February 1982, March 1981 and November 1977 in the Bransfield Strait and adjacent waters were investigated. Juveniles in November 1977 fed mainly on calanoid copepods and Oithona spp. The principal food of postlarvae in February 1982 were Oncaea spp., eggs of calanoid copepods and tintinnids whereas the staple food of juveniles in February 1982 consisted of calanoid copepods of which copepodites of Calanus propinquus were most abundant. Eggs of Euphausia superba were frequently ingested by postlarvae and were the main component of the juvenile diet in the Antarctic Sound. Postlarvae in March 1981 preyed on Oncaea spp. and calanoid eggs. There was a shift from feeding on cyclopoid copepods by postlarvae to feeding on calanoids by juveniles. The food particle size increased as a function of fish length. Maximum prey size was controlled by mouth width up to at least 45 mm standard length. Prey selection was apparently food density dependent with an inverse relationship between food abundance and selective feeding. Density dependent size selection may have resulted in resource partitioning among postlarval and juvenile fishes in February. This specific feeding behaviour is likely to be an adaptation to the low zooplankton stocks of the high Antarctic shelf waters to minimize food competition among the youngest age classes. Predation on krill eggs indicated that the frequent association of one year old juvenile Pleuragramma antarcticum with the Antarctic krill is related to local spawning events.